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Income Taxes (Components) (Details) - CAD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017
Components of Income Tax Expense (Benefit), Continuing Operations [Abstract] |  |
Deferred income taxes | $ 185 | $ 469
Income tax expense (recovery) | 69 | 520
Income Tax Reconciliation Revaluation Of US Non Regulated Deferred Income Taxes | 0 | 317
Supplemental Tax Information [Abstract] |  |
Income before provision for income taxes | 816 | 819
Income taxes, at statutory income tax rates | 253 | 254
Canada [Member] |  |
Components of Income Tax Expense (Benefit), Continuing Operations [Abstract] |  |
Current income taxes | 3 | 24
Deferred income taxes | 11 | 3
Operating loss carry forwards | (33) | (40)
Supplemental Tax Information [Abstract] |  |
Income before provision for income taxes | 127 | 88
United States [Member] |  |
Components of Income Tax Expense (Benefit), Continuing Operations [Abstract] |  |
Current income taxes | (121) | 24
Deferred income taxes | 211 | 384
Operating loss carry forwards | 0 | (194)
Supplemental Tax Information [Abstract] |  |
Income before provision for income taxes | 646 | 693
Other [Member] |  |
Components of Income Tax Expense (Benefit), Continuing Operations [Abstract] |  |
Current income taxes | 2 | 3
Deferred income taxes | (3) | (1)
Operating loss carry forwards | (1) | 0
Supplemental Tax Information [Abstract] |  |
Income before provision for income taxes | $ 43 | $ 38

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